Gas fired heating system



y 8, 1956 G. N. MILES 2,744,517

GAS FIRED HEATING SYSTEM Filed Oct. 20, 1951 lNVENTOR.

Unite GAS FKRED HEATING SYSTEM Application Uctober 20, 1951, Serial No.252,268

3 Claims. (Cl. 126-110) This invention relates to improvements inheating systems, and particularly to an improved gas supply for a gasfired heating system.

In U. S. Patent 2,579,507 of C. D. MacCracken, there is described aheating system utilizing a combustible gas as a fuel. While not limitedthereto, the present invention finds particular application in and willbe described herein with special reference to a heating system of thetype described in the foregoing copending application.

In practically all gas fired heating systems, the fuel supply lineleading to the burner includes a main valve which is usually controlledby a thermostat or the like. Ordinarily, of course, it is anticipatedthat the control valve will function properly to shut off the gas supplywhen the valve is closed. However, it is always possible that this valvemay fail to close properly, or that it will be open when cooperatingparts of the system are inactive, with the result that some gas may flowto the burner when the, system is intended to be shut down, withpossible attendant hazards.

In systems of the type described in the above-mentioned copendingapplication, for example, the gas from the main burner normally isignited by an electrical igniter or spark plug. Of course, when thesystem is shut down, the igniter Will not be energized. Under suchconditions, gas leakage may build up an explosive concentration in thesystem that could he accidentally ignited withundesirable results. Insystems wherein ignition of the gas is by means of a continuouslylighted pilot burner, a similar situation may develop if the pilot flamegoes out and the main burner valve fails to close tightly.

Aside from the danger of explosion, a leaking main control valve mayalso result in the seepage of raw gas into the rooms of the house orother enclosure being heated by the system. This is especially true inforced draft systems, and particularly where both combustion andventilating air are supplied by a common blower as in the system of theabove-mentioned copending application. In such systems, when the bloweris shut off there is a more or less direct path from the burner backthrough the air inlet to the ventilating air ducts. Of course, theundesirable features of having raw gas escape into the rooms intended tobe heated need not be explained.

It is, therefore, a general object of the present invention to providean improved fail-safe gas supply for a gas fired heating system. A morespecific object of the invention is to provide an improved arrangementfor removing from a gas fired heating system any gas that may leak pastthe main control valve when the latter is intended to be closed. Anotherobject of the invention is to provide a simple, automatic vent valvearrangement for a gas fired heater.

In accordance with the invention, the foregoing and other relatedobjects of the invention are attained by the provision of anautomatically valved gas supply control, downstream of the main controlvalve, that selectively directs gas either to the burner or to a bypassoutlet lead- States Patent ing to the furnace flue. In accordance with apreferred embodiment of the invention, the control arrangement includesa Venturi fitting that directs the gas flow in response to the conditionof a pressure actuated valve in a venting bypass line.

A more complete understanding of the invention, and of further objectsand advantages thereof, can be had by reference to the followingdescription of illustrative embodiments thereof when considered inconnection with the accompanying drawing, wherein Fig. 1 is a schematicdiagram of a gas fired heating system arranged in accordance with theinvention, and

Fig. 2 is a partially schematic and partially cross-sectional diagramshowing specific flow control means suitable for use, in accordance withthe invention, in the system of Fig. 1.

Referring to Fig. 1 of the drawing, there is shown a gas-fired furnacegenerally similar to that shown and described in the above-mentionedcopending MacCracken application. The furnace of Fig. 1 includes aburner 10 comprising a perforated cylindrical casing 12 defining acombustion chamber 14. A nozzle 22 at the end of a gas supply pipe 23extends into a mixing tube 24. The mixing tube 24 leads to burner ports26 in the inlet end of the casing 12. Adjustable air ports 28 may beprovided at the inlet end of the mixing tube 24 to admit primarycombustion air to the mixing tube, wherein the primary combustion airand gaseous fuel will be thoroughly mixed before passing through theburner ports 26. A spark plug 30 is provided in one wall of the casing12 for igniting the gaseous fuel mixture.

A blower or fan 18 is provided in an air duct 19 leading to the burnerto supply pressurized air both for the burner 10 and for ventilatingpurposes as explained hereinafter.

A cylindrical sleeve 21 surrounding the casing 12 is spaced therefrom todefine a uniform inlet path for secondary combustion air to flow to thecombustion chamber 14 through holes 20 in the casing 12. If desired, themixing tube 24 can be omitted, in which case all of the combustion airwill be supplied through the holes 20.

At the outlet end of the combustion chamber 14, heat exchange surfaces33 of a heat exchanger 34 define a combustion gas passageway 32 leadingto an outlet fiue 36.

Part of the pressurized air supplied by the blower 18 will flow througha duct 38 to pass in heat exchange relationship over the surfaces 33 inthe heat exchanger and thence out to the space to be heated in the usualmanner.

As thus far described, the heating system shown in Fig. 1 is more orless conventional. Certain features of the system should be noted,however, because of their special relation to the present invention.

There will normally be only a very slight draft in the flue 36 when theblower 18 is not operating. Such draft as may exist in the flue will bepractically unnoticeable in the combustion chamber 14. Furthermore, whenthe blower 18 is off, there will be a relatively direct path from thecombustion chamber 14 through the holes 21 into the duct 19 and thencethrough the duct 38 and the heat exchanger 34 into the space to beheated. Therefore, it can be seen that if any gas were to flow into theburner 10 when the blower 18 is not operating, one could not assume thatsuch gas would pass harmlessly out the flue 36. In fact, it is'quitelikely that the gas would fiow through the duct 33 and heat exchanger 34into the space to be heated. If leaking gas did not pass out of theburner, then a concentration of raw gas might well be built up in thecombustion chamber 14 that would be explosive.

In accordance with the present invention, provision is made in the gassupply system of the furnace to avoid the foregoing possibilities. As isusual, the supply system includes a gas inlet line 40 having a maincontrol valve 42 therein. The control valve 42 may be any one of anumber of different types of valves conventionally used for turning onand off the supply of combustible fuel to the burner. In the presentinstance, it will be assumed that the valve 42 is electrically operated,under the control of a thermostat (not shown) or the like. On thedown-stream side of the control valve 42, a Venturi fitting 74 isprovided to direct gas either through the line 23 leading to the gasnozzle 22 or through a bypass line 48 leading to the outlet fiue 36,depending on the setting of a valve 84 in the bypass line. Preferably,the valve 84 is controlled by the pressure in the casing 19, as sensedthrough a line 100.

As shown, the bypass line 48 can conveniently be connected to the outerhood of the conventional draft diverter 37. This arrangement has theadvantage that any condensate forming in the flue 36 due to rapidtemperature changes therein will not find its way into the bypass line48.

One specific arrangement of parts embodying the invention, as shown inFig. 2, includes a Venturi fitting 74 connected between the down-streamside of the main control valve 42, the feed line 23 and the bypass line48. The Venturi fitting 74 comprises a casing having an inlet port 76, afirst outlet port 78 and a second outlet port 89. A tapered nozzle 82inside the casing 74 extends from the inlet port 76 to somewhat beyondthe second outlet port 80.

in the bypass line 48, there is provided a pressure actuated valvecomprising a hollow casing 84 having a diaphragm 86 therein dividing theinterior of the casing 84 into upper and lower chambers, 88 and 90,respectively. 1 An inlet port 92 and an outlet port 94 are provided forthe upper chamber 88, while a single inlet port 96 is provided for thelower chamber 90. An annular skirt 98 inside the upper chamber 88surrounds the first inlet port 92 and terminates adjacent the diaphragm86 to define an internal extension of the inlet port 92 adapted to beclosed by the diaphragm 86.

A pipe 100 leads from the lower chamber inlet port 96 to the air duct19. The outlet port 94 in the upper chamber of the valve communicateswith the bypass line 48 leading to the flue 36.

In the operation of the system shown in Figs. 1 and 2, the blower 18 andthe main control valve 42 normally will be related in their operation sothat there will be a substantial amount of pressure in the duct 19 whenthe valve 42 is open. Pressurized air in the duct 19 will becommunicated by the connecting line 100 to the lower chamber 95* of thepressure actuated valve 84. This pressurized air acting against thelarge lower face of the diaphragm 86 will be more than adequate toovercome the gas pressure against the relatively small central sectionof the upper side of the diaphragm 86. Consequently, the diaphragm 36will seal off the line leading to the bypass 48, and gas will flow fromthe nozzle 82 downwardly into the feed line 23. However, when the blower18 is not operating, there will be no pressure in the duct 19 to holdthe diaphragm 86 against the skirt 98. Consequently, the diaphragm 86will move downwardly, opening a path for gas flow through the bypassline 48. Accordin ly, if the main control valve 42 fails to operateproperly when the system is shut down, or if there is any gas llow forany reason in the absence of blower pressure, such gas will flow out ofthe nozzle 82 into the line 78 and through the valve 84 and bypass theline 48 to the outlet fiue 36. This flow of gas will have an aspiratingeffect which will create a slight suction at the lower outlet port 80 ofthe Venturi fitting 74. Consequently, it will be impossible for any gasto V flow downwardly through the feed line 23 to the burner,

and in fact any gas in the line 23 when the blower stops operating willbe withdrawn and pass out the flue.

From the foregoing, it can be seen that the present invention provides avery simple arrangement for automatically controlling gas input to a gasfired heating system in an efiieient and reliable manner.

What is claimed is:

1. In a heating system of the type utilizing as the fuel a combustiblegas and comprising (1) a burner, (2) an outlet flue communicating withsaid burner to carry away gaseous combustion products therefrom, and (3)a combustible gas supply system including an inlet line and a valve insaid inlet line, the improvement which comprises a Venturi fittingcomprising (1) a body having an inlet opening communicating with saidline on the downstream side of said valve, said body also having two outlet openings, one of said outlets being substantially in coaxialalignment with said inlet opening and the other of said outlets beingbetween said inlet and said one outlet and offset from said inlet, and(2) a nozzle inside said body extending from said inlet opening to apoint beyond said other outlet, a line connecting said other outletopening to said burner, a third line connecting said one outlet openingto said fiue, and valve means in said third line for closing and openingsaid third line, whereby to direct gas passing said first-named valve tosaid burner when said third line is closed and to said flue when saidthird line is opened.

2. In a warm air gas-fired furnace of the type comprising (l) acombustible gas burner unit including means defining a combustionchamber, (2) a heat exchanger having surfaces defining a combustion gaspassageway in communication with said burner to receive hot combustionproducts therefrom, (3) an outlet fine communicating with saidpassageway, (4) a blower communicating with said combustion chamber tosupply pressurized air thereto, (5) means communicating with said blowerto distribute ventilating air from said blower over said surfaces toheat said ventilating air, (6) a gas inlet line having a valve therein,the improvement which comprises a Venturi fitting comprising (1) a bodyhaving an inlet opening communicating with said line on the downstreamside of said valve, said body also having two outlet openings, one ofsaid outlets being substantially in coaxial alignment with said inletopening and the other of said outlets being between said inlet and saidone outlet and offset from said inlet, and (2) a nozzle inside said bodyextending from said inlet opening to a point beyond said other outlet, aline connecting said other outlet opening to said burner, a normallyopen second valve, a third line connecting said one outlet opening tosaid flue through said second valve, and means in said sec ond valvecommunicating with said blower and responsive to pressurized air fromsaid blower to close said normally open valve.

3. In a warm air gas-fired furnace of the type comprising (l) acombustible gas burner unit including means defining a combustionchamber, (2) a heat exchanger having surfaces defining a combustion gaspassageway in communication with said burner to receive hot combustionproducts therefrom, (3) an outlet flue communieating with saidpassageway, (4) a blower communicating with said combustion chamber tosupply pressurized air thereto, (5) means communicating with said blowerto distribute ventilating air from said blower over said surfaces toheat said ventilating air, (6) a gas inlet line having a valve therein,the improvement which comprises a Venturi fitting comprising (1) a bodyhaving an inlet opening communicating with said line on the downstreamside of said valve, said body also having two outlet openings, one ofsaid outlets being substantially in coaxial alignment with said inletopening and the other of said outlets being between said inlet and saidone outlet and offset from said inlet and .(2) a nozzle inside said bodyextending from said inlet opening to substandaily opposite said otheroutlet, a line connecting said other outlet opening to said burner, asecond valve comprising a hollow body having a diaphragm thereindividing the interior of said body into first and second chambers, saidbody having therein a first inlet port communieating with said firstchamber and a second inlet port communicating with said second chamber,an annular skirt inside said first chamber surrounding said first inletport and terminating adjacent said diaphragm to define an internalextension of said first port adapted to be closed by said diaphragm,said body further having an outlet port communicating with said firstchamber, a line connecting said first port to said one outlet opening, aline connecting said outlet port to said flue, and a line con- 6 meetingsaid second chamber to said blower to cause said diaphragm to close saidfirst port in response to pressurized air received from said blower.

References Cited in the file of this patent UNITED STATES PATENTS341,628 Archer May 11, 1886 1,519,673 Doble Dec, 16, 1924 2,062,605Peters Dec. 1, 1936 2,424,154 Dunham July 15, 1947 2,547,735 Blaha Apr.3, 1951 2,646,789 Lampert July 28, 1953

